Thermochemistry of aluminum species for combustion modeling from ab initiomolecular orbital calculations

High accuracy ab initio methods for computational thermochemistry have been applied to aluminum compounds expected to be present during combustion of aluminum particles. The computed enthalpies of formation at 298.15 It agree well with experimental values from the literature for AlCl, AlCl3, AlO, Al OAl, linear OAlO, planar Al2O2, AlOH, AlH, and AlN. The agreement is fair f or AlCl2. Major revisions to the recommended thermochemistry must be consid ered for OAlCl, OAlH, OAlOH, and AlC. This is not surprising since the ther modynamic data for OAlCl, OAlN, OAlOH, and AlC are given in the literature as rough estimates. Calculated thermochemical data are also presented for s everal species never studied experimentally including AlH2, AlH3, AlOO, cyc lic-AlO2, linear AlOAlO, AlHCl, AlHCl2, and others. Based on the performanc e of the CBS-Q and G2, methods observed in other systems, the calculated en thalpies of formation would be expected to be accurate to within +/-1 to 2 kcal mol(-1). However, relatively large differences between the results fro m the CBS-Q and G2 methods for the aluminum oxides indicate that the uncert ainties are slightly larger for these compounds. The thermochemistry propos ed here is shown to predict substantially different equilibrium composition from the thermochemistry previously available in the literature. (C) 2000 by The Combustion Institute.